Water-soluble cellulose derivatives in smoking products



United States Patent WATER-SOLUBLE CELLULOSE DERIVATIVES IN SMOKING PRODUCTS Walter G. Frankenburg, Millersville, Pa., assignor to General Cigar Co., Inc., New York, N. Y., a corporation of New York No Drawing. Application July 19, 1949, Serial No. 105,660

20 Claims. (Cl. 131-17) This invention relates to tobacco products adapted for smoking, and more particularly to smoking products in which a water-soluble cellulose derivative is used in conjunction with tobacco.

In copending patent application, Serial No. 720,682, of Frankenburg and Garbo, filed January 7, 1947, now abandoned in favor of a continuation application that eventuated in U. S. Patent 2,592,553, dated April 15, 1952, there is disclosed a process for preparing coherent masses of comminuted tobacco by mixing the comminuted tobacco with a limited quantity of an aqueous solution of a water-soluble derivative of cellulose, particularly an ether of cellulose like methyl cellulose or carboxymethyl cellulose, to form a paste which is pressed or rolled into sheets, rods and the like. The thus formed coherent masses of tobacco are then dried and are ready for utilization in cigar-making machines or in any other desired manner. As pointed out in that application, such tobacco products are surprisingly free of the obnoxious qualities and properties associated with tobacco products obtained by the many proposals of the prior art wherein the method of combining comminuted tobacco and a binding agent or the selected binding agent or both the method and the binding agent differ from the method and binding agents taught by the aforesaid copending application. While numerous smoking tests have shown that the average smoker is satisfied with the smoking qualities of cigars made up with sheets formed from tobacco particles and a water-soluble cellulose ether as binding agent, it has been found that a small percentage of the smokers who have an unusually keen taste for or sensory response to tobacco smoking detect in smoking these tobacco products containing water-soluble cellulose derivatives the presence of a small amount of a foreign material which is variously reported as being woody, aldehydic or acidic. The success of large commercial-scale manufacture of cigars or other smoking products depends today on giving complete smoking pleasure to not only the average smoker but also the smoking connoisseur. Accordingly, considerable effort has been devoted to finding ways and means for making tobacco products containing watersoluble cellulose derivatives fully acceptable to the entire smoking fraternity. To state it in another way, research has been directed to making smoking products containing tobacco and water-soluble cellulose binders which in smoking characteristics are not perceptibly different from smoking products containing the same tobacco without the cellulose binders.

In one of its aspects, the present invention is in the nature of an improvement of the process and products of the aforementioned copending application.

The primary object of this invention is to provide improved smoking products comprising tobacco and watersoluble cellulose derivatives.

Another principal object is to provide smoking products comprising tobacco and water-soluble cellulose binders which are free of the undesirable by-taste of the smoke derived from the burning of the cellulose binders.

These and additional objects and advantages of the present invention Will be apparent from the description which follows.

In accordance with this invention, a smoking product in which tobacco is present in conjunction with a watersoluble cellulose derivative has incorporated therein a finely divided, siliceous, mineral-type material which being incombustible remains substantially unchanged throughout the burning process and functions like a catalyst in modifying the combustion of the cellulose derivative so that the resultant combustion gases and vapors are substantially free of the undesirable components formed when the cellulose derivative is burned in the absence of the siliceous material. Thus, the tobacco product in spite of the presence of an extraneous, combustible substance, namely, the water-soluble cellulose derivative, is in smoking pleasure not perceptibly different, even to the smoking connoisseur, from a product made with the same tobacco but without the cellulose derivative.

Pursuant to one of the most valuable embodiments of this invention, leaf tobacco which has been processed by drying, curing, sweating, fermenting, aging and similar treatments preparatory to its utilization in the manufacture of cigars and like products is comminuted, in a dry state, in any of several well-known types of dry grinders or pulverizers. The tobacco, which may include stems or midribs, is generally ground to such a degree that at least about by weight of the ground tobacco will pass through an 80-mesh screen and a substantial portion will have a particle size which is finer than the openings of a ZOO-mesh screen. Considerably coarser and finer tobacco powders are, however, utilizable. The comminuted tobacco is then converted into a plastic mass by thoroughly mixing the dry powder with a limited quantity of a highly viscous aqueous solution of a watersoluble derivative of cellulose.

The quantity of aqueous solution of cellulose derivative which is admixed with the powdered tobacco is limited to that which yields a plastic mass having a consistency approximating that of a good neat cement mortar. An excess of solution detectable by the tendency of the plastic mass to exude liquid should be avoided since any substantial loss of liquid reflects a loss of extractable constituents in the tobacco and consequent alteration of the original smoking qualities of the tobacco. Even when soluble constituents are extracted from powdered tobacco with water and the extract is not permitted to become separated from the tobacco paste, impairment of the original properties of the tobacco occurs because the soluble constituents of the tobacco rapidly undergo undesirable reactions while in the extract form. The highly viscous aqueous solutions of cellulose derivative used in this invention are such poor extracting agents that the ordinary injury to tobacco, as it occurs by the leaching effect of water, is almost completely averted. Usually, one part by Weight of comminuted tobacco and about two to six parts by weight of the aqueous solution of cellulose derivative will form a paste of the desired consistency.

As already stated, to the combination of tobacco and cellulose binder there is added a finely divided, siliceous, mineral-type material which has the property of modifying the combustion of the cellulose binder so that a smoker can no longer detect the acidic or other undesirable smoke components developed in the ordinary combustion of the cellulose derivative. Typical suitable siliceous materials are acid-treated clays, heat-treated montmorillonite, and natural and synthetic silicates containing some hydrogen atoms which are relatively mobile. Inasmuch as these siliceous materials are not combustible and yet exert a favorable influence on the burning of Water-soluble cellulose derivatives, I believe that they act as catalysts in the sense that the usual aldehydic or acidic or hydrocarbon-type products of combustion are not at all formed or, if formed, are promptly further oxidized to the harmless form of carbon dioxide and water vapor so that the smoker observes no foreign taste or odor. For want of a better term, suitable siliceous inaterials will hereinafter be referred to as siliceous cataysts.

The siliceous catalysts of this invention are not to be confused with the typical combustion catalysts that have been suggested hitherto for use in tobacco products. Strangely enough, such combustion catalysts like the finely dispersed oxides of iron, copper or other heavy metals or alkali metal salts have proved worthless in overcoming the undesirable smoke components formed when a watersoluble cellulose derivative is burned. On the other hand, extensive tests with various siliceous catalysts have revealed a striking parallelism between their effectiveness for the purposes of this invention and their effectiveness as petroleum cracking catalysts. In short, there is a well defined trend indicating that a siliceous catalyst which is good for cracking hydrocarbons is good for avoiding the development of objectionable smoke components in smoking tobacco products containing water-soluble cellulose derivatives. In fact, I have prepared very satisfactory smoking products made up of tobacco and water-soluble cellulose binders by incorporating therein siliceous catalysts selected merely on the basis that they were known to be successful cracking catalysts of the petroleum refining industry. This surprising discovery may indicate that the pyrogenic decomposition products of the watersoluble cellulose derivatives are similar, or identical with, hydrocarbons and that the function of the siliceous catalyst consists in cracking these hydrocarbons into smaller molecular units which are them readily and completely oxidized to carbon dioxide and water vapor.

The siliceous catalysts of this invention are also not to be confused with water-swelling bentonite or similar clay as disclosed in the aforesaid patent of Frankenburg and Garbo. As brought out in that patent, the bentonite on swelling in the wet plastic mass of tobacco and cellulose derivative tends to form a coherent inorganic skeleton or reinforcing network which improves the physical properties of the final product. In contrast thereto, the siliceous catalysts effective for the purpose of this invention are non-water-swelling.

It is today generally accepted that a certain acidic nature is essential for the effectiveness of catalysts for cracking high molecular hydrocarbons to lower molecular fragments. This property also seems to be a prerequisite for the efficiency of the siliceous catalysts used pursuant to my invention for the improvement of odors developed in igniting cellulose derivatives, such as methyl cellulose or carboxymethyl cellulose. A class of catalysts with the proper acidic nature which can be used is that of solid particles containing silica and such amounts of difficultly reducible metal oxides that the molecular ratio of silica to the other oxides exceeds appreciably the value of 1. As all these combinations of silica with other oxides, such as for instance, alumina, zirconia, titania, chromium oxide, magnesium oxide and others, contain small amounts of water, it is quite likely that the solid phase comprises a kind of complex acid in which some hydrogen atoms are in a rather mobile state especially at the surface of the solid particles. This view and experimental support for it have been presented by R. C. Hansford in a paper entitled, A mechanism of catalytic cracking, Ind. and Eng. Chem., 39, 849 (1947). The specific catalyst mentioned in this paper was composed of approximately 12% alumina and 88% silica (on dry basis). In another paper entitled, Montmorillonite cracking catalyst, Ind. and Eng. Chem., 41, 1485 (1949), Alexander Grenall has demonstrated the presence of hydrogen ion in Filtrol clay catalysts.

Silica gels which have been impregnated, even with as little as 1% alumina, have been shown to be eflicient cracking catalysts by Pitzer in Advancing Fronts in Chemistry," vol. 1, page 33, 1945, Rheinhold Publishing Corp. Another cracking catalyst has been described by OKelly et al. in Ind. and Eng. Chem., 39, 154 (1947), as being prepared by the co-precipitation of the hydrous oxides of silicon and aluminum in a weight ratio of 9:1 of silica to alumina. A tri-component cracking catalyst consisting of silica, alumina and zirconia has been described by Thomas et al. in J. Chem. Soc., 66, 1694 (1944).

Cracking catalysts can be prepared by using natural clays as a starting material. Many clays contain silica and alumina in a ratio which corresponds to the postulate that the number of moles of silica exceed appreciably the number of moles of alumina or other oxide. However, some of these clays contain, instead of mobile hydrogen atoms combined with excess silica, other atoms, such as alkali and alkaline earth atoms. Such clays can be activated by removing part or all of the alkali and alkaline earth atoms and replacing them with hydrogen atoms by treatment with acid. Other clays, which already in their original composition have a potential acidic nature by having the proper ratio of silica to alumina or other oxides, can be activated by heat treatment (cf. Alexander Grenall, l. c.).

All of the aforementioned natural and synthetic cracking catalysts are effective siliceous catalysts for the purposes of this invention. To recapitultae, my siliceous catalyst is a combination of a major weight proportion of silica and a minor weight proportion of one or more difficultly reducible metal oxides; this combination may be effected synthetically or it may be derived from natural materials like clays through activation by heat and/ or acid treatment.

Reverting to the embodiment of the invention in which comminuted tobacco is combined with a viscous aqueous solution of a cellulose binder to yield a nonexuding plastic mass, the siliceous catalyst is added to the aqueous solution of the cellulose binder before or after or simultaneously With the addition of powdered tobacco. In short, the order of addition is not important; the important point is that the siliceous catalyst particles are wetted and enveloped by the solution of cellulose binder.

The sheet or other coherent form containing the comminuted tobacco, the water-soluble cellulose binder and the siliceous catalyst is dried to any desired moisture content. The water is evaporated at moderate temperatures usually not exceeding about 50 C. The resulting coherent, self-supporting tobacco product may then be fed to a cigar-making machine or used in any other desired manner.

From the foregoing description, it is obvious that the tobacco has not lost any of its constituents during processing nor has it been subjected to any harmful conditions, such as water extraction, elevated temperatures or strong acids or bases. Also, in accordance with my invention, two very important precautions are taken to ensure acceptance of my new tobacco products by even the most discriminating smokers, viz., (l) the proportion of cellulose binder in the tobacco product is kept small so that, if the product did not have the siliceous catalyst, the smoke taste and other characteristics of the product would differ only slightly from those of the tobacco itself and (2) the addition of a small but effective quantity of siliceous catalyst is made to influence the burning of the water-soluble cellulose derivative so that the slight difference in smoking enjoyment, which might otherwise be noticed by smokers with keen tastes and which is attributable to the combustion of the cellulose derivative, is no longer discernible.

As used in this specification and the appended claims, the term, water-soluble derivative of cellulose, means any water-soluble derivative of cellulose composed solely of carbon, hydrogen and oxygen atoms. Advantageously, such a derivative is of the type represented by the formu a:

Cellulose radical solubilizing radical showing an ether linkage between the cellulose radical and the solubilizing radical. In the formula, n is a number corresponding to the number of cellulose units in the particular cellulose used, x is a number not greater than 3 depending upon the number of hydroxyl groups in the cellulose unit replaced by ether-linked solubilizing radicals and Q is a radical containing 1 to 4 carbon atoms, preferably 2 carbon atoms. Generally, when the radical Q contains 2 or more carbon atoms, the more oxygen atoms there are in the radical Q, the better it is for the purposes of this invention; oxygen present in the form of -OH groups is particularly desirable. Representative water-soluble derivatives of cellulose successfully used in this invention are:

Methyl cellulose (CGH'102(OH)3-m)n (O CH3 m- Carboxymethyl cellulose (CeHwOz (OH) 3-1) 11. (O CH2 COOH) :cn' Hydroxyethyl 6811111086 (CSH'IOZ OH)3-x) n (O CH2 CH2OH In It is well to note that in the production of certain watersoluble derivatives, for instance, hydroxyethyl cellulose by the reaction between alkali cellulose and ethylene oxide, the reactant furnishing the solubilizing radical to the cellulose may at the same time undergo polymerization with the result that the cellulose derivative formed may comprise solubilizing radicals which are polymeric in structure. In other words, the radical Q may be composed of a multiplicity of molecular units each containing 1 to 4 carbon atoms in contrast to a single molecular unit,

for instance, the single unit -CI-Iz-CHzOH shown above in the formula for hydroxyethyl cellulose. Water-soluble derivatives of cellulose in which the solubilizing radicals have a polymeric structure are useful for the purposes of this invention. Where the water-soluble derivative of cellulose has an acid grouping as in the case of carboxymethyl cellulose, it may be used in the form of the corresponding salt, usually the sodium or potassium salt, and the prior statement that the water-soluble derivative of cellulose is composed solely of carbon, hydrogen and oxygen is not intended to exclude the water-soluble salts, e. g., alkali metal salts, of acid-type derivatives of cellulose. At any given temperature and concentration, the viscosity of the aqueous solution of a cellulose derivative will vary with the molecular complexity or weight of its cellulose radical (factor n) as well as with the degree of etherification (factor x). In the foregoing formulae, the factor n is a convenient means used to indicate the polymeric nature of cellulose.

The invention contemplates the use of mixed watersoluble derivatives of cellulose not only in the sense of mixtures of two or more separate and different derivatives but also in the sense of single derivatives having two or more different substituents associated with the cellulose. Thus, in accordance with the first sense, a mixture of equal parts by weight of methyl cellulose and sodium salt of carboxymethyl cellulose may be employed as the binding agent for tobacco products prepared in accordance with this invention. In the other sense, suitable binders are high viscosity grades of single, watersoluble cellulose derivatives having two or more different substituents, which may be exemplified by a cellulose derivative of the type of methyl ethyl cellulose or ethyl hydroxyethyl cellulose. It is well to observe that in a water-soluble cellulose derivative with two or more different substituents not all of the substituents need to be substituents or radicals which exert a solubilizing effect on cellulose when dispersed in water. For example, a mixed cellulose ether might have a relatively small proportion of hexyl radicals serving as one substituent and a relatively large proportion of carboxymethyl radicals serving as the solubilizing substituent. In further connection with the thought that the cellulose need not be heavily substituted to yield a water-soluble derivative adapted for the purpose of this invention, it is interesting to note that the sodium salt of carboxymethyl cellulose used in the examples presented hereinafter is reported to have only 0.4 to 0.6 carboxymethyl group for each anhydroglucose unit of the cellulose molecule or, in other words, for each cellulose radical of the type formula shown hereinafter.

From the foregoing it is clear that cellulose ethers which are water-soluble and form highly viscous solutions are particularly useful in this invention. However, the invention is not limited to such ethers and contemplates the use of any suitable water-soluble cellulose derivative, e. g., cellulose esters made up entirely of carbon, hydrogen and oxygen atoms, which yields a highly viscous aqueous solution.

A water-soluble cellulose derivative suitable for the purposes of this invention is one which gives a viscosity of at least 1500 centipoises at a temperature of C. when not more than about 2% by weight thereof is dissolved in water; preferably, the cellulose derivative yields an aqueous solution of equal or greater viscosity when present in only about 1% concentration. These cellulose derivatives not only must dissolve in water and yield at low concentrations highly viscous solutions but also must be capable of forming a coherent, tough sheet or mass when their aqueous solutions are evaporated to dryness. The behavior of the cellulose derivative in solution facilitates the preparation of the plastic mass containing the finely divided tobacco as well as the subsequent pressing and shaping of the mass into desired forms. The physical characteristics of the cellulose derivative as deposited from its aqueous solution contribute cohesiveness and flexibility to the tobacco product after it has been dried and conditioned to a desirable moisture content. The tobacco products of this invention contain not more than 13% of the cellulose derivative based on the weight of the tobacco. The preferred tobacco products contain about 8% to 12% of cellulose derivative based on the weight of the tobacco.

The smoking compatibility of water-soluble cellulose derivatives and tobacco should be safeguarded by the exercise of care in selecting cellulose derivatives in a state of refinement. The refined products should be free of any appreciable quantities of extraneous matter contaming compounds of nitrogen, sulfur, phosphorus and the halogens; in short, compounds giving undesirable products of combustion or of dry distillation should be avolded.

The quantity of siliceous catalyst required in the tobacco products of this invention depends upon the efficacy or activity of the chosen siliceous catalyst and the propensity of the selected cellulose derivative to give off acidic or other undesired gases during combustion. In general, the addition of the siliceous catalyst falls in the approximate range of 20% to 60% based on the weight of cellulose derivative in the tobacco product. The preferred siliceous catalysts, like good hydrocarbon cracking catalysts, are usually employed in the proportions of about 45% to 55% based on the weight of cellulose derivative used in the tobacco product.

It is often advisable, where the product of this invention is made in sheet form and is later rolled or bent sharply as in making cigars, that the product contain a plasticizer to increase the flexibility and cracking resistance of the sheet. Additions of glycerine of the order of 5% to 20% by weight, based on the weight of dry tobacco used, to mixtures of comminuted tobacco and aqueous solutions of cellulose derivatives exert an appreciable plasticizing effect. The presence of glycerine in these amounts in the tobacco product does not lead to the formation of unpleasant or troublesome products of complete or incomplete combustion. In the cigarette industry, glycerine is frequently used as a humectant in the tobacco without adverse effects from the viewpoint of smoking. Sorbitol may be substituted for at least part of the plasticizing glycerine.

In the interests of better understanding and greater clarity, illustrative embodiments of the invention are presented hereinbelow in detail. In these examples, which are not to be construed in any restrictive sense, the proportions mentioned are all based on a common weight unit.

Example 1 A highly viscous (about 4000 cps. at 25 C.) solution was prepared by dissolving 11 parts of methyl cellulose (Dow Methocel-4000 cps. type) in 550 parts of water. To this solution were added 5 parts of glycerine and 3 parts of sorbitol. Wisconsin cigar leaf tobacco ground to particles chiefly in the size range of 80 to 200 mesh was mixed with the solution to form a consistent paste; parts of the tobacco powder was used. An addition of 5 parts of powdered siliceous catalyst, having a particle size of less than 200-mesh, was incorporated in the paste. Specifically, the siliceous catalyst was a silica gel containing about 11% by weight of alumina (ground Sovabead catalyst of Socony-Vacuum Oil Company). The .pasty mass which showed no tendency to exude liquid on standing was placed on a plate of polished stainless steel and covered with a sheet of wax paper. With the aid of a roller, the mass was pressed out between the wax paper and steel plate into a layer about & inch thick. The wax paper was removed and the plastic layer was permitted to dry overnight by exposure to room air (about 25 C.). The air-dried tobacco sheet was used in place of the conventional binder leaf in the manufacture of cigars. Smoking tests revealed that the product had a pleasant aroma and burned satisfactorily. Sensitive smokers who had previously complained of acidic and irritating smoke components in smoking tests with a product substantially identical with that of the instant example except for the omission of the siliceous catalyst were no longer able to detect such foreign smoke components when smoking the tobacco product of this example.

Example 2 A very viscous (of the order of 50,000 cps. at 25 C.) solution was prepared by dissolving 11 parts of the sodium salt of carboxymethyl cellulose (Hercules CMC high viscosity type) in 430 parts of water. To this solution, 16 parts of glycerine were added. One hundred parts of a Wisconsin cigar leaf tobacco, ground so that approximately 70% by weight passes through a 200- mesh screen and less than 2% is retained on an 80-mesh screen, were added to the viscous aqueous solution along with 5 parts of finely powdered (finer than 200-mesh size) siliceous catalyst, which was a thermally activated montmorillonite clay (Filtrol X-202 clay cracking catalyst of Filtrol Corporation). The entire dough-like mass was mixed thoroughly and then placed in an extrusion machine to produce a ribbon, about ,1 inch in thickness and 3 inches wide. The extruded ribbon of tobacco paste was deposited on a moving band of wire cloth and dried while on this band by means of a dry air stream at a temperature of 50 C. The ribbon was thus dried to a moisture content of about 20% by weight, yielding a coherent tobacco sheet useful in the manufacture of cigars and other smoking products. Comparative smoking tests, as in Example 1, showed that the siilceous catalyst eliminated the acidic smoke components ordinarily produced in the burning of carboxymethyl cellulose. In short, the tobacco product of this example was entirely acceptable to very discriminating smokers.

Example 3 A highly viscous (about 4000 cps. at 25 C.) solution was prepared by dissolving 11 parts of methyl cellulose (Dow Methocel-4000 cps. type) in 550 parts of water. To this solution were added 16 parts of glycerine and 100 parts of ground tobacco consisting of 30 parts of Wisconsin cigar leaf, 56 parts of Pennsylvania cigar leaf and 14 parts of Havana cigar leaf. The screen analysis of the ground tobacco was 2.8% by weight retained on an 80-mesl1 screen and 82% passing through ZOO-mesh. To the resulting, nonexuding paste, there was added 5.5 parts of finely powdered siliceous catalyst, a thermally activated montmorillonite clay (Super Filtrol F0 clay cracking catalyst of Filtrol Corporation). As in Example 1, after all the components had been thoroughly mixed to give a uniform paste, the mass was formed and dried into a thin sheet. Comparative smoking tests made it clear that the product of this example was free of the complaints of sensitive smokers who noted the presence of unpleasant foreign components in the smoke derived from a product lacking the siliceous catalyst but otherwise the same as the product of this example.

The foregoing class of tobacco product in which finely divided tobacco, a water-soluble cellulose binder and a siliceous catalyst are brought together to form coherent bodies like sheets, ribbons and rods may include fine glass fibers as a component to improve the physical properties of my tobacco products. My copending application, Serial No. 692,775, filed on August 24, 1946, now U. S. Patent 2,592,554, issued April 15, 1952, teaches that tobacco sheets or like bodies formed from a paste of comminuted tobacco and a viscous aqueous solution of a suitable binder are more resilient and flexible if fine glass fibers are incorporated in the paste. Fine glass fibers of the order of 0.0002" in diameter resembling silk threads not only in appearance but also in softness and flexibility are employed in the proportion of about 1% to 15% based on the weight of the tobacco; preferably, about 2% to by weight of glass fibers are combined with the finely divided tobacco. The glass fibers may be used in the form of loose fibers or in the form of very thin fiber mats. If matted glass fibers are employed, the paste comprising tobacco powder, water-soluble cellulose binder, water and siliceous catalyst may be spread or otherwise applied to one or both sides of the thin mat of glass fibers. The tobacco-coated mat of glass fibers is then dried to give a strong, flexible tobacco sheet which is particularly well suited for feeding into cigar-making machines wherein the tobacco sheet is used as the binder leaf of the cigars.

While the description of my invention has been presented hereinbcfore largely in terms of the embodiment wherein comminuted tobacco is formed into coherent, continuous bodies like sheets with the aid of a watersoluble derivative of cellulose, it is obvious that the advantages of my discovery of siliceous catalysts to modify beneficially the burning of water-soluble cellulose derivatives are applicable to any other type of smoking tobacco product which contains such a cellulose derivative. To illustrate, cigarettes may be manufactured in which the conventional paper covering is replaced by a film made from a water-soluble cellulose derivative. By incorporating a siliceous catalyst in the film prepared from a water-soluble cellulose derivative, the novel cigarettes will burn satisfactorily without permitting the cellulose derivative to give off the usual irritating vapors and gases. If desired, a white pigment such as titanium dioxide or calcium carbonate may be added along with the siliceous catalyst to the highly viscous aqueous solution of a cellulose derivative from which the film is made; thus the white film will resemble the white paper covering which it replaces in this new type of cigarette.

As a further illustration, tobacco leaves may be joined with one another by lapping the leaves along their edges and using a highly viscous aqueous solution of a cellulose derivative as the binding agent between the overlapped tobacco leaves. In this way, it is possible to form a continuous sheet from individual tobacco leaves and the incorporation of a siliceous catalyst in this product will prevent the evolution of undesirable combustion gases from the cellulose derivative when cigars or like smoking products made from this type of sheet are burned in the course of smoking.

In all cases, it is well to remember that the selected water-soluble cellulose derivative must have a viscosity of at least 1500 centipoises at a temperature of 25 C. when not more than about 2% by weight thereof is dissolved in water and must be used in a proportion not exceeding 13% of the weight of the tobacco. Under such circumstances, the incorporation of siliceous catalysts pursuant to this invention results in smoking tobacco products having the advantages already described.

It should be observed that while the tobacco products of this invention are made with water-soluble cellulose derivatives, the finished products may ultimately have the water-soluble celluose derivatives in an insolubilized state because of natural or induced reactions. For instance, a tobacco sheet, prepared by mixing powdered tobacco with a highly viscous aqueous solution of the sodium salt of carboxymethyl cellulose to yield a consistent paste and by rolling the paste out into a thin layer, may be partially insolubilized by the tannins in the tobacco and partially by applying a polyvalent metal salt, e. g., a calcium, aluminum or magnesium salt, to the tobacco layer. It is obvious that, after the tobacco product has been compounded and pressed into the desired form, such insolubilization of the water-soluble cellulose derivative used as the binding agent is not detrimental but rather is beneficial because the binding agent will not be redissolved by the saliva of smokers and will therefore better withstand disintegration of the coherent mass of comminuted tobacco.

Those skilled in the art will visualize many other modifications and variations of the invention set forth hereinabove without departing from its spirit and scope. Accordingly, the claims should not be interpreted in any restrictive sense other than that imposed by the limitations recited within the claims.

What I claim is:

1. An improved smoking tobacco product comprising a predominant proportion of dry-ground tobacco, a minor proportion, not exceeding about 13% by weight of said tobacco, of a water-soluble cellulose derivative capable of forming a solution with a viscosity of at least 1500 centipoises at a temperature of 25 C. when not more than about 2% by weight of said cellulose derivative is dissolved in water, said cellulose derivative functioning to hold the particles of said tobacco together as a coherent mass, and a minor proportion of a non-water-swelling siliceous catalyst to suppress the evolution of undesirable gases from said cellulose derivative during the smoking of said tobacco product, said siliceous catalyst being dispersed in and enveloped by said cellulose derivative and amounting to at least about 20% by weight of said cellulose derivative.

2. The product of claim 1 wherein the water-soluble cellulose derivative is a cellulose ether and the siliceous catalyst is a hydrocarbon cracking catalyst, synthetically prepared and consisting essentially of a major weight proportion of silica and a minor weight proportion of at least one difficultly reducible metal oxide.

3. The product of claim 1 wherein the water-soluble cellulose derivative is an alkali metal salt of carboxymethyl cellulose and the minor proportion of siliceous catalyst is in the range of about 20% to 60% by weight of said carboxymethyl cellulose.

4. The product of claim 1 wherein the water-soluble cellulose derivative is methyl cellulose and the minor proportion of siliceous catalyst is in the range of about 20% to 60% by weight of said methyl cellulose.

5. The product of claim 1 wherein the water-soluble cellulose derivative is a cellulose ether capable of forming a solution with a viscosity of at least 1500 centipoises at a temperature of 25 C. when not more than about 1% by weight of said cellulose ether is dissolved in water.

6. The product of claim wherein the water-soluble cellulose ether is an alkali metal salt of carboxymethyl cellulose and the siliceous catalyst is a hydrocarbon cracking activated clay present in an amount in the range of about 45% to 55% by weight of said carboxymethyl cellulose.

7. The product of claim 5 wherein the water-soluble cellulose ether is methyl cellulose and the siliceous catalyst is a hydrocarbon cracking activated clay present in an amount in the range of about 45 to 55% by weight of said methyl cellulose.

8. In the manufacture of smoking tobacco products from tobacco and a water-soluble cellulose derivative, used as a binding agent for said tobacco, the improvement of dispersing a finely divided non-water-swelling siliceous catalyst substantially uniformly in said cellulose derivative, while said cellulose derivative is dissolved in water, to suppress the evolution of undesirable gases from said cellulose derivative during the smoking of said tobacco products, said siliceous catalyst amounting to at least about 20% by weight of said cellulose derivative.

9. The process of claim 8 wherein the siliceous catalyst is a hydrocarbon cracking catalyst consisting essentially of a major weight proportion of silica and a minor weight proportion of at least one difiicultly reducible metal oxide.

10. The process of claim 9 wherein said cellulose lderivative is an alkali metal salt of carboxymethyl celluose.

11. The process of claim 9 wherein said cellulose derivative is methyl cellulose.

12. A novel cigarette comprising a film of a watersoluble cellulose ether as the outer covering thereof and a finely divided non-water-swelling siliceous catalyst embedded in said film to suppress the evolution of undesirable gases from said film during the smoking of said cigarette.

13. The novel cigarette of claim 12 wherein the watersoluble cellulose ether is methyl cellulose.

14. In tobacco smoking products, the improvement of a binding agent as a component of said smoking products comprising a water-soluble cellulose derivative in film form and a finely divided non-water-swelling siliceous catalyst dispersed in and enveloped by said cellulose de rivative to suppress the evolution of undesirable gases from said cellulose derivative during the smoking of said smoking products, said siliceous catalyst amounting to at least about 20% by weight of said cellulose derivative.

15. The tobacco smoking products of claim 14 wherein the water-soluble cellulose derivative is a cellulose ether and the siliceous catalyst is a hydrocarbon cracking catalyst, synthetically prepared and consisting essentially of a major weight proportion of silica and a minor weight proportion of at least one difficultly reducible metal oxide.

16. The tobacco smoking products of claim 14 wherein the water-soluble cellulose derivative is methyl cellulose and the siliceous catalyst is a hydrocarbon cracking activated clay.

17. In tobacco smoking products wherein tobacco particles are held together by a water-soluble cellulose derivative, the weight proportion of said cellulose derivative being minor to that of said tobacco particles, the improvement of a finely divided non-water-swelling siliceous catalyst dispersed in and enveloped by said cellulose derivative to suppress the evolution of undesirable gases from said cellulose derivative during the smoking of said smoking products, said siliceous catalyst amounting to at least about 20% by weight of said cellulose derivative.

18. The tobacco smoking products of claim 17 wherein the water-soluble cellulose derivative is a cellulose ether and the siliceous catalyst is a hydrocarbon cracking catalyst consisting essentially of a major weight proportion of silica and a minor weight proportion of at least one difiicultly reducible metal oxide.

19. The tobacco smoking products of claim 18 wherein the cellulose ether is an alkali metal salt of carboxymethyl cellulose and the siliceous catalyst does not exceed about by weight of said carboxymethyl cellulose.

20. The tobacco smoking products of claim 18 wherein the cellulose ether is methyl cellulose and the siliceous catalyst does not exceed about 60% by weight of said methyl cellulose.

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1. AN IMPROVED SMOKING TOBACCO PRODUCT COMPRISING A PREDOMINANT PROPORTION OF DRY-GROUND TOBACCO, A MINOR PROPORTION, NOT EXCEEDING ABOUT 13% BY WEIGHT OF SAID TOBACCO, OF A WATER-SOLUBLE CELLULOSE DERIVATIVE CAPABLE OF FORMING A SOLUTION WITH A VISCOSITY OF AT LEAST 1500 CENTIPOISES AT A TEMPERATURE OF 25* C. WHEN NOT MORE THAN ABOUT 2% BY WEIGHT OF SAID CELLULOSE DERIVATIVE IS DISSOLVED IN WATER, SAID CELLULOSE DERIVATIVE FUNCTIONING TO HOLD THE PARTICLES OF SAID TOBACCO TOGETHER AS A COHERENT MASS, AND A MINOR PROPORTION OF A NON-WATER-SWELLING SILICEOUS CATALYST TO SUPPRESS THE EVOLUTION OF UNDESIRABLE GASES FROM SAID CELLULOSE DERIVATIVE DURING THE SMOKING OF SAID TOBACCO PRODUCT, SAID SILICEOUS CATALYST BEING DISPERSED IN AND ENVELOPED BY SAID CELLULOSE DERIVATIVE AND AMOUNTING TO AT LEAST ABOUT 20% BY WEIGHT OF SAID CELLULOSE DERIVATIVE. 